Microwave antenna lobing device



Jan. 28, 1958 KIYO TOMIYASU MICROWAVE ANTENNA LOBING DEVIQE 2 She ets-Sheet 1 v Filed Jui 19, 1954 v w l K LVENTOR N 0 0 0 'Y/ISU ATTORNEY Jan. 28, 1958 KIYO ToMlYAsu 2,821,712

' MICROWAVE ANTENNA LOBING DEVICE:

Filed July 19,1954 2 Sheets-Sheet 2 TTORNEY Unitid Stems atent MICROWAVE ANTENNA LOBING DEVICE Kiyo Tomiyasn, Flushing, N. Y., assignor to Sperry Rand Corporation, a corporation of Delaware Application July 19, 1954, Serial No. 443,996 9 Claims. (Cl. 343-854) This invention relates to a microwave antenna system, and, more particularly, is concerned with means for transmitting sequentially produced asymmetrical electromagnetic radio beams having space patterns which are mirror images of one another.

Transmitting systems providing alternately energized overlapping space lobes are employed in aircraft locators, direction finders, and instrument landing systems. Particularly in the latter case, it is desirable that the individual field patterns of the overlapping lobes have an asymmetrical configuration to provide broad coverage in the off-course region and to provide sharp cut-ofi in the on-course region where the lobes overlap, the two lobes having space patterns which are substantially mirror images of each other.

' Various methods and schemes have been employed in the prior art for providing overlapping asymmetrical lobes of this type. For example, one common scheme is to provide a pair of radiating horns which are designed to provide the desired space pattern, and alternately switching the transmitter to the two horns. Another known scheme, of which the present invention may be considered a modification, is shown in the copending application Serial No. 302,401, filed August 2, 1952, in the name of Bernard Berkowitz by the assignee of the present invention. In that invention asymmetrical overlapping lobes are produced by the use of a continuously energized compound-type horn structure. The lobes are alternately produced by phase switching means which.

periodically shifts the phase of one component of energy relative to a second component of energy radiated by the compound-type horn structure.

It is a general object of this invention to provide an improved radiating system for producing overlapping lobes having asymmetrical space patterns.

Another object of this invention is to provide means for alternately producing a pair of overlapping asymmetri cal radio beams radiated from radiator.

Theseand other objects of the invention which will become apparent as the description proceeds are achieved a single simple horn by the provision of apparatus comprising a single horn to which energy is coupled by means of a section of rectangular wave guide dimensioned to propagate energy in the TE and TE modes at the frequency of operations Means, including a mode converter couples energy in the TE mode to the wave guide section from a source of microwave energy. Separate means including a phase shifter couples energy in the TE mode to the wave guide section from the microwave source. The energy propagated in the TE mode is fed to the horn in phase quadrature with respect to the energy in the T13 mode,

the phase shifter introducing periodically a 180 phase shift, whereby the energy in the TB mode alternately leads and. lags in phase the energy in the TE mode..-

For a better understanding of the invention, reference hou d be had, to the a c mp nyin dra ings. r in:

ice

Fig. 1 is a side elevational view of the radiating structure of the present invention;

Fig. 2 is a plan view of the same radiating structure shown in Fig. 1;

Fig. 3 is a cross-sectional view taken on the line 3-3 of Fig. 2;

Fig. 4 is a graphical plot of the electric field intensity as a function of position across the mouth of the horn;

Fig. 5 is a rectangular coordinate plot of the resulting far-field space pattern showing the energy measured in decibels as a function of angular deviation from a line perpendicular to the plane of the horn aperture;

Fig. 6 is a side elevational view of a modification of the present invention;

Fig. 7 is a plan view partially in section of the mode converter used in the modification of Fig. 6; and

Fig. 8 is a cross-sectional view taken substantially on the line 88 of Fig. 6.

Withparticular reference to the form of the invention shown in Figs. 1 and 2, the numeral 10 indicates generally a source of microwave energy, such as, for example, the transmitter of an instrument landing system. Energy from the microwave source 10 is coupled to the input portion of an adjustable power divider 11, which may be of any suitable type such as a hollow pipe wave guide Y-junction having a movable fiap 12 for changing the ratio of energy transmitted to the two output portions of the junction. The position of flap 12 is controlled by a knob 14.

Energy from the lower output portion of the divider 11 is coupled to a phase switch indicated generally at 16. One suitable switch includes a motor 18 which drives a disc 20, the disc being provided around its periphery with a plurality of spokes. The spokes pass through gaps in each of the wave guide sections or branches 22 and 24, and are so positioned that when a spoke enters the gap in one of the wave guide sections, the other wave guide section is open to permit transmission of energy therealong. A switch of this type is described in detail in Patent No. 2,544,715 to R. B. Muchmore. As the motor 18 rotates, the transmission path of the energy is changed in length, the lower wave guide branch 24 being a half wavelength or integral multiple thereof greater in length than the wave guide branch 22. Thus the switch 16in effect shifts the phase of the energy at the output thereof 180 at a periodic rate.

.The output from the switch 16 is coupled to a section 25 of wave guide which includes a portion at one end thereof of increased .width, as indicated at 26. The broad dimension of the wave guide in the region 26 is such as to support a TE mode of propagation at the frequencyof the source 10. The section of wave guide 25 in turn is coupled to the input of a horn 28.

Energy from the upper output portion of the divider 11 passes through a twisted wave guide section 30, in which theplane of the E-vector is rotated to an adjustable phase sihfter 32, which is preferably of a type described in Patent No. 2,630,492 to R. B. Muchmore. The purpose of the phase shifter is to provide means of adjusting the relative phase of the two components of energy propagated in the two branches of the transmis Fig. 3, the action of the T-junction between the wave 282L712 Patented Jan. 28, 1958- .pattern is a Gaussian-like pattern.

upper: branch of the Y-junction-1-1 into the-wider-portion-.=

26 of the wave guide 25, ins-sthe TE mode of propagation. The arrows in Fig. 3 indicate the electric field configurationin the region -of-'t'he-' jujrretion-. Thustwo co1nponents of energy in two modes of propagation-,hzrtnely; the TEi mode-as der-ived from-thelower btanchof the Y-junction 11 and energy in the TE mode as derived from the-upper branch of the Y-junction '11, are-propagated in the wide region 26 of the wave guide 25 to the born 28.

If the TE mode component "of the energyradiated from the horn is in phase-quadrature with respect to the TE- mode componentof the energy radiated from the born, the resulting space pattern will be the algebraic sum of the componentpatterns-resulting from the two modes. The phase quadrature relationship can be introduced by the difference in path length for the twocom ponents and may be more closely adiusted by means 'of the phase shifter 32. The energy distribution across the mouth of the horn produced'by the T13 mode component is symmetrical, as indicated by the curve 40 of the graphical plot of Fig. 4, which is a plot of the electric intensity across the mouth of the horn. The energy distribution across the mouth of the horn due to the TE mode component is shown by the curve 42 of Fig. 4. The curve 40 approximates a Gaussian function while the curve 42 approximates a Rayleigh function, which is-the derivative of the Gaussian function. It is the known property'of radiators, that an illumination resembling the Gaussian or Rayleigh functions produces a far-field pat-- tern following the same function. Thus, the anti-sym metric component of the far-field pattern is a Rayleighlike pattern, and the symmetric component of the far-field Moreover, the sum of these functions at the aperture of a horn, regardless of the ratio of energy levels therein, yields a space pattern resembling the algebraic sum of the two components.

Therefore with the horn aperture having energy components illuminating the aperture approximately accord-' ing to the Gaussian and Rayleigh functions, the far-field pattern can be readily found by adding algebraically the two curves 40 and 42 of Fig. 4, which also represent the far-field component patterns. The result is an asymmetrical space pattern, as shown by the curve 44 of Fig. 5. By reversing the phase of the energy'of one component, for example the symmetrical component of energy at the horn, as by means of the phase switch 16, the mirror image of the far-field space pattern, as indicated by the dotted line 46, is produced. Thus the periodic reversal of phase by the switch 16 produces the, desired beam lobing effect.

Referringto Fig.6, an "alternative arrangement to that of Figs. 1 and 2 is shown. Again the energy from a source 10 is divided into two portions by a ,Y-junction 11', one portion being coupled bya 180 phase shifting switch 16 to a born 28 through one arm 50 of a directional coupler indicated generally at 52. The broad dimension of the arm 50 of the coupler 52 is such as to transmit energy in the TE mode at the operating frequency of the system.

The other portion of energy from the divider 11 is:

coupled to a mode converter, indicated generally at '54,- which converts the energy from the TB mode to the TE mode. A suitable mode converter is shown in Fig. 7 and includes a section of wave guide 56 which is widened at one-end so as to support energy in the TB mode. A septum 58 is provided in the wide portion of the wave guide section 56 and a block dielectric material 60"is positioned within the wave guide 56 on one side of. the septum 58, the dielectric} block 60 being such as to introduce a 180 phase shriftinthe compbnentofenergy' transmitted thereby.- The; resultis that in the regions-be yond the sepnumthe; energy :is propagatedtintthe TE mode.- Suchmode; cenuertersaaremellthe; priest-t 75 pics thereof being taught in Patent No. 2,129,669 to A. E.

The energy thus converted to the TE mode is coupled to the horn 28 through the directional coupler 52 through the second arm 62 thereof. As seen in the sectional view of Fig. 8, the directional coupler 52 is provided with a narrow slot 64 in the common wall between the arms 62 and 50 of the coupler 52'. The length of the slot 64 wants :to be such as to effect substantially %'-transfer of energy transmitted in the TE mode from the arm 62 into the arm 50 of the coupler 52. For this purpose the length of the slot should be approxiamtely 1.8x, where h is the. wavelength at the operating frequency.

Thus. as in the modification of Figs. 1 and 2, two components of energy are transmitted to the born 28, namely a TE mode component which provides a symmetrical Gaussian-type distribution of energy across the mouth of the horn, and a TE mode component which provides an anti-symmetric Rayleigh-type energy distribution across the mouth of the horn. The result is an asymmetrical space pattern, the mirror image of which can be produced by shifting the phase of one component by as by the phase shifting switch 16.

From the above description it will be seen that the various obiects of the invention have been achieved by the provision of beam transmitting apparatus for alternately producing overlapping lobes having asymmetrical space patterns which can be radiated from a single conventional-type horn. It should be noted that. although the present invention has been particularly described as a radiating system, it may be readily adapted for use as. a. directional receiving system as well.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter con-,

TB mode to the wave guide section from the source,

means including mode converting means for coupling a second component of energy in the TE mode to the wave guide section from the source, the first and second componentsof energy in the wave guide section being in phase quadrature, means for periodically switching the relative phase between the first and second components of energy in the wave guide section by 180, and a horn radiator coupled to ,the wave guide section.

2. Apparatus for radiating a radio beam having an asymmetrical. space pattern, said apparatusv comprising a source of microwave energy, a section of rectangular wave guide dimensioned to propagate the TE and TE modes of, propagation at the. frequency of the source, means .for couplinga first component of energy in the TB mode to the. wave guide section from the source, means including mode converting ,meansfor simultaneously coupling a second component of energy in the TE mean'sefor-tcoupling a firs't component of energy-in uts TE mode to the wave guide section from the source, means for simultaneously coupling a second component of energy in the TE mode to the wave guide section from the source, the first and second components of energy in the wave guide section being in phase quadrature, and means coupled to the wave guide section for simultaneously radiating the first and second components of energy.

4. Apparatus for radiating a radio beam having an asymmetrical space pattern, said apparatus comprising a source of microwave energy, a section of rectangular wave guide dimensioned to prop-agate the T13 and TE modes of propagation at the frequency of the source, means for coupling a first component of energy in the TE mode to the wave guide section from the source, means for simultaneously coupling a second component of energy in the TE mode to the wave guide section from the source, means for periodically shifting the relative phase of 'said first and second components of energy, and means coupled to the wave guide section for simultaneously radiating the first and second components of energy.

5. Ultra high frequency apparatus comprising a source of microwave energy, a wave guide junction including a first section of rectangular wave guide, a portion of which is expanded in width to support the TE mode of propagation at the frequency of the source and a second section of rectangular wave guide coupled to a broad wall of the first section in a T-junction, the second section being oriented with the broad walls thereof lying in planes parallel to the longitudinal axis of the first section, whereby "energy in the second section is coupled into the first section in the TE mode of propagation, means coupling a first component of energy from the source to the first section of the junction, means coupling a second com.- ponent of energy from the source to the second section of the junction, means associated with one of said source coupling means for periodically switching the relative phase of said first and second components of energy by 180, said first and second components of energy being in phase quadrature at the wave guide junction, and means coupled to the wide portion of the first section of the junction for simultaneously radiating said first and second components of energy. a

6. Ultra high frequency apparatus comprising a source of microwave energy, a wave guide junction including a first section of rectangular wave guide, a portion of which is expanded in width to support the TE2Q mode of propagation at the frequency of the source and a second section of rectangular wave guide coupled to a broad wall of the first section in a T-junction, the second section being oriented with the broad walls thereof lying in planes parallel to the longitudinal axis of the first section, whereby energy in the second section is coupled into the first section in the TE mode of propagation, means coupling a first component of energy from the source to the first section of the junction, means coupling a second component of energy from the source to the second section of the junction, said first and second components of energy being in phase quadrature at the wave guide junction, and means coupled to the wide portion of the first section of the junction for simultaneously radiating said first and second components of energy.

7. Ultra high frequency apparatus for directionally transmitting or receiving microwave energy, said apparatus including a first section of rectangular wave guide,

one end portion of which is expanded in width to support the TE mode of propagation at the operating frequency, a second section of rectangular wave guide, the first and second sections being coupled together at each end thereof to form two propagation paths in parallel, one end of the second section being joined in a T-junction to a broad wall in the expanded width portion of the first section, the second section at the junction being oriented with the broad walls thereof parallel to the longitudinal axis of the first section, means connected in series with one of said sections for periodically changing the phase relation between the components of energy propagated in the two sections, and horn means connected to the first section at said one end portion thereof.

8. Ultra high frequency apparatus for directionally transmitting or receiving microwave energy, said apparatus including a first section of rectangular wave guide, one end portion of which is expanded in width to support the TE mode of propagation at the operating frequency, a second section of rectangular wave guide, the first and second sections being coupled together at each end thereof to form two propagation paths in parallel, the second section having one end portion thereof expanded in a width to support the TE mode of propagation at the op erating frequency, mode converting means in series With the second section between said end portion and the rest of the section, directional coupling means including the wide portions of said first and second sections, said portion having a common broad wall therebetween, the broad wall having a longitudinally extending narrow coupling slot therein for directionally coupling energy in the TE mode of propagation between the two sections of wave guide, means connected in series with one of said sections for periodically changing the phase relation between the components of energy propagated in the two sections, and horn means connected to the first section at said one end portion thereof.

9. Ultra high frequency apparatus for directionally transmitting or receiving microwave energy, said apparatus including a first section of rectangular wave guide, one end portion of which is expanded in width to support the TE mode of propagation at the operating frequency, a second section of rectangular wave guide, the first and second sections being coupled together at each end thereof to form two propagation paths in parallel, the second section having one end portion thereof expanded in width to support the T13 mode of propagation at the operating frequency, mode converting means in series with the second section between said end portion and the rest of the section, directional coupling means including the wide portions of said first and second sections, said portion having a common broad wall therebetween, the broad wall having a longitudinally extending narrow coupling slot therein for directionally coupling energy in the TE mode of propagation between the two sections of wave guide, and horn means connected to the first section at said one end portion thereof.

Hughes et 211.: Proceedings of the I. R. 15., vol. 37, No. 9, September 1949, page 1031. 

